The present invention relates to the art of electromechanical relays and, more particularly, to an improvement in an electromechanical latch relay having a manual reset mechanism.
The invention finds particular utility in connection with a double throw relay and accordingly will be described in detail with respect thereto. At the same time, however, the invention is adapted to be used in other electromechanical reset relays of the type which are latched in response to energization of the relay coil and manually unlatched or returned to a reset position.
Electromechanical relays have been provided heretofore with mechanisms for latching the relay closed when energized and requiring manual release of the latch to reset the relay. Such relays are widely used in a variety of electrical systems wherein it is desired, for example, to open a circuit to electrical equipment to render the latter inoperative in response to a fault and to require manual reclosing of the circuit following correction of the fault. A variety of relays of the foregoing type and for the foregoing purposes have been provided heretofore, such as those shown in prior U.S. Pat. Nos. 3,614,684 to Agler and 4,097,832 to Ritzenthaler et al, which two patents are incorporated by reference herein for background information. In these two patents there is disclosed a reciprocable latch-reset member which is spring biased in response to energization of the relay coil and displacement of the relay armature thereby to latch the armature in the displaced position independent of coil energization. When the coil is de-energized, displacement of the latch-reset member in the direction against the spring bias releases the relay armature for displacement back to the initial or reset position thereof.
Such a relay can be used, for example, in an electrical circuit for controlling electrical equipment such as a motor so as to open the circuit thereto in response to a fault. In this respect, the latter circuit is normally closed to energize the motor, and the relay coil is energized in response to the occurrence of a fault to open the circuit to the motor and, in a double throw relay, to close a normally open auxiliary circuit such as an alarm circuit to provide a visual or audible signal indicative of the fault condition. The alarm circuit is often remotely located with respect to the electrical equipment whereby, if the alarm circuit is defective or if the relay is defective with respect to closing the alarm circuit, a fault can go undetected for a considerable period of time. While the circuit to the electrical equipment may be opened in response to the fault, early detection and correction of the fault condition may be critical to prevent damage to the electrical equipment or other equipment with which it is associated. Furthermore, while a visual or audible alarm circuit has been referred to as being closed in conjunction with the opening of a circuit to electrical equipment, it will be appreciated that an auxiliary function circuit could be closed in response to a fault or other relay control signal, whereby a defect in the auxiliary circuit, or the relay contacts closing the same, would result in the auxiliary function not being achieved.
Accordingly, it becomes desirable to provide the relay with a testing mode, independent of actuation thereof by energization of the relay coil, to enable testing the operability of the relay in connection with the alarm, auxiliary function, or other circuit closed thereby in response to opening the normally closed main circuit. The two aforementioned United States patents do not provide a testing mode for the relays shown therein, and the only known arrangement heretofore provided in conjunction with such relay structures requires the use of a plunger member separate from the latch-reset member for displacing the relay armature toward the coil independent of coil energization. The latter arrangement, in addition to requiring at least one additional component part and a support structure therefor in the relay assembly, results in displacement of the latch-reset member into the latching position relative to the relay armature. Therefore, the latch-reset member must be manually displaced to achieve return of the armature to the reset position following a test function. Such resetting is often overlooked, whereby time is lost in having to return to the location of the relay to reset the same before the main circuit can function. This disadvantage is in addition to such relays being expensive to manufacture and requiring two manual operations to be performed to achieve a test.